Laboratory Medicine & Hematology & Family Medicine
Fibrinogen
Fibrinogen (coagulation factor I) is a soluble plasma glycoprotein synthesized exclusively by the liver, playing a central role in both blood coagulation and the inflammatory response. With a molecular mass of around 340 kDa, it is composed of three pairs of polypeptide chains (Aα, Bβ and γ) linked by disulfide bridges, and circulates in plasma at a concentration of 2 to 4 g/L in healthy adults. Its role in coagulation is fundamental: under the action of thrombin (generated at the end of the coagulation cascade), fibrinogen is cleaved into fibrin monomers, which spontaneously polymerize into a soluble fibrin network, then stabilized by factor XIIIa into insoluble fibrin, forming the definitive framework of the clot. Polymerized fibrin also retains activated platelets and red blood cells to form a strong, resistant thrombus. Beyond coagulation, fibrinogen is a major acute-phase protein - its plasma concentration increases 2-10-fold in response to inflammation, infection, trauma and neoplasia - under the effect of pro-inflammatory cytokines (mainly IL-6). This dual nature - coagulation factor and inflammatory marker - makes the interpretation of fibrinogen particularly rich but also complex: high fibrinogen may reflect chronic inflammation or increased cardiovascular risk, while low fibrinogen in an acute context is an alarm signal of consumption (DIC) or severe liver failure. The plasma half-life of fibrinogen is 3 to 5 days, making it a relatively sensitive indicator of acute coagulation variations.
Normal values, dosage and clinical interpretation
- Normal values and assay methods : normal adult values: 2.0-4.0 g/L (200-400 mg/dL) - physiological variations: newborn: 1.5-3.0 g/L (slightly lower) - pregnancy (3rd trimester): 4.0-6.0 g/L (significant physiological increase from 2nd trimester onwards - important to know when interpreting fibrinogen in an obstetrical context) - elderly: tendency towards moderate physiological elevation (3.5-5.0 g/L) linked to chronic low-grade inflammation; Clauss method (functional method - gold standard): measures the clotting time of diluted plasma in the presence of excess thrombin - result expressed in g/L - reflects functionally active fibrinogen - reference method recommended by ICSH - sensitive to the presence of anticoagulants (heparin + AOD at high concentrations can bias the result downwards); PT-derived fibrinogen : mathematical calculation from prothrombin time - less accurate than Clauss's method - overestimates fibrinogen in dysfibrinogenemia - not recommended as primary method; immunoassay (fibrinogen antigen): measures total fibrinogen (functional + non-functional) - useful for diagnosing dysfibrinogenemia (functional fibrinogen/antigen ratio <0.7 → dysfibrinogenemia)
- Low fibrinogen - causes and clinical orientation : fibrinogen <2.0 g/L: hypo-fibrinogenemia threshold - fibrinogen <1.0 g/L: clinically significant hemorrhagic risk - fibrinogen <0.5 g/L: almost certain spontaneous bleeding - replacement urgency; acquired low fibrinogen causes: DIC (disseminated intravascular coagulation) - most frequent and urgent cause: massive consumption of fibrinogen by generalized pathological activation of coagulation - context: severe sepsis + major trauma + acute promyelocytic leukemia (APL/M3) + retroplacental hematoma + amniotic embolism + snakebite - fibrinogen often <1.0 g/L + prolonged PT + prolonged APTT + thrombocytopenia + very high D-dimers → ISTH score DIC; severe hepatocellular failure: the liver is the only site of fibrinogen synthesis - decompensated cirrhosis + fulminant hepatitis + advanced hepatocellular carcinoma → collapse of synthesis → fibrinogen <1.5 g/L; primary fibrinolysis (without DIC): plasminogen activation without prior activation of coagulation - cirrhosis + prostate surgery + administration of thrombolytics (rtPA + streptokinase + urokinase) - distinguished from DIC by absence of thrombosis + moderately elevated D-dimer + accelerated clot lysis time; massive hemodilution: massive transfusions + crystalloid/colloid infusions in intensive care - fibrinogen is the first coagulation factor to become critical upon dilution (critical threshold reached before PT and APTT); hereditary causes (rare): afibrinogenemia (total absence - autosomal recessive - biallelic FGA/FGB/FGG mutations - severe bleeding from birth) + hereditary hypofibrinogenemia + dysfibrinogenemia (low functional fibrinogen but normal antigen - heterozygous mutations - paradoxical risk of thrombosis in certain forms)
- Elevated fibrinogen - causes and cardiovascular risk : fibrinogen >4.0 g/L: hyperfibrinogenemia - most often reactive (acute phase); frequent causes of elevated fibrinogen: acute and chronic inflammation (bacterial infections + chronic inflammatory diseases : RA + IBD + lupus + spondyloarthritis) + neoplasia (tumor inflammation marker + some cancers secrete fibrinogen directly) + trauma and surgery + nephrotic syndrome (increased compensatory hepatic synthesis) + pregnancy (physiological up to 6 g/L in 3rd trimester) + smoking (significant hyperfibrinogenemia - pro-inflammatory + pro-atherogenic mechanism) + obesity + type 2 diabetes + hypothyroidism ; high fibrinogen and cardiovascular risk : meta-analysis Danesh et al. 2005 (JAMA - Fibrinogen Studies Collaboration - 154,211 patients): each 1 g/L increase in fibrinogen associated with a 54 % increase in risk of coronary heart disease and a 51 % increase in risk of stroke - independent of other risk factors - however, fibrinogen is not recommended for routine cardiovascular screening (no specific treatment targeting fibrinogen other than correction of risk factors); acquired dysfibrinogenemia : moderate hepatic insufficiency (structurally abnormal + quantitatively increased fibrinogen) + monoclonal gammopathy (interference with fibrin polymerization)
Clinical situations and management
| Clinical situation | Interpretation and further assessment | Care and treatment |
|---|---|---|
| DIC - disseminated intravascular coagulation Hematological emergency - fibrinogen <1.5 g/L |
DIC is the most feared hematological emergency associated with low fibrinogen - it results from pathological and generalized activation of coagulation beyond normal regulatory mechanisms; ISTH open DIC score (Score of International Society on Thrombosis and Haemostasis): platelets: >100 G/L = 0 + 50-100 = 1 + <50 = 2; D-dimer or PDF: not elevated = 0 + moderately elevated = 2 + very elevated = 3; prolonged PT: 6 s = 2; fibrinogen: ≥1 g/L = 0 + <1 g/L = 1 - score ≥5 = open DIC - score 3-4 = incipient DIC (check daily); biological work-up DIC: CBC + PT + APTT + fibrinogen (Clauss) + D-dimer + PDF (fibrin degradation products) + blood smear (schizocytes - microangiopathy) + liver workup + LDH + haptoglobin (hemolysis) - repeat every 4-6h in acute phase; triggering causes to be identified and treated urgently: Gram-negative sepsis (LPS) + acute promyelocytic leukemia (APL - release of tissue factor and fibrinolytic enzymes) + obstetrical complications (retroplacental hematoma + amniotic embolism + fetal death in utero) + severe trauma + extensive burns + venomous snakebite | Treatment of DIC: treatment of the underlying cause (absolute priority) - without etiological treatment, DIC cannot be controlled; fibrinogen replacement: fibrinogen target >1.5-2.0 g/L in case of active bleeding or impending invasive procedure - human fibrinogen concentrate (RiaSTAP - Fibryga): initial dose 30-50 mg/kg IV over 15-30 min - 1 g of fibrinogen concentrate increases fibrinogenemia by around 0.25 g/L - advantage over fresh frozen plasma (FFP): reduced volume + high concentration + no risk of volume overload; fresh frozen plasma (FFP): 10-15 mL/kg - provides fibrinogen + all other coagulation factors - useful if multiple factor deficiency (DIC with very prolonged PT + APTT); cryoprecipitate (if available): rich in fibrinogen (+ factor VIII + vWF + factor XIII) - 1 pool of 5 units → increase fibrinogen by 0.5-1.0 g/L; platelet transfusion: if platelets <50 G/L + active bleeding → threshold <20 G/L without bleeding; tranexamic acid (Cyklokapron): anti-fibrinolytic - 1 g IV over 10 min + 1 g/h × 8h - indicated if predominant fibrinolytic component (surgery + trauma) - caution if DIC with predominant thrombosis; heparinotherapy in DIC: controversial - reserved for predominantly thrombotic DIC (purpura fulminans + LAP after initiation of treatment) under close hematological monitoring |
| Post-partum obstetric hemorrhage Fibrinogen - an early marker of severity |
Fibrinogen is the earliest coagulation marker and the most predictive of the severity of postpartum hemorrhage (PPH) - its value at the time of PPH diagnosis predicts the risk of progression to severe PPH with an excellent negative predictive value; Charbit et al. study. 2007 (Journal of Thrombosis and Haemostasis): fibrinogen 4 g/L → negative predictive value of 79 % for absence of progression; clinical action thresholds in PPH: fibrinogen >4 g/L : reassuring - monitoring + standard PPH management; fibrinogen 2-4 g/L: monitor + repeat dosing every 30-60 min + prepare for transfusion; fibrinogen <2 g/L: transfusion of fibrinogen concentrate or cryoprecipitate urgently - target ≥2.0 g/L; important physiological context: fibrinogen is physiologically high in late pregnancy (4-6 g/L) - a fibrinogen level of 2 g/L in a parturient therefore represents a dramatic 50-70 % drop in pregravid values - the absolute value must be interpreted in the light of this baseline elevation; complete hemostatic workup in severe PPH: CBC + PT + APTT + fibrinogen + D-dimer + thromboelastography (TEG) or thromboelastometry (ROTEM) if available - ROTEM enables rapid, global assessment of coagulation at the patient's bedside (results in 5-10 min) | Transfusion protocol in severe PPH: activation of massive transfusion protocol (MTP) if losses >1,500 mL or hemodynamic instability - RGC:FFP:platelet ratio guided by TEG/ROTEM or in absence of viscoelastometry: ratio 1:1:1 (1 RGC + 1 PFC + 1 platelet pool); fibrinogen concentrate as 1st line if fibrinogen <2 g/L: dose 2-4 g IV (30-50 mg/kg) - short preparation time (5-10 min) vs PFC (thawing 20-30 min) - decisive advantage in the context of active bleeding; tranexamic acid (Cyklokapron) : 1 g IV as soon as PPH is diagnosed (within 3 h of delivery - WOMAN trial 2017 Lancet) - reduces bleeding mortality by 19 % - routinely administered without waiting for biological results; uterotonics: oxytocin 10 IU IV + misoprostol 800 µg sublingual/rectal + methylergometrine + carboprost (Hemabate) according to protocol stage; surgery and interventional radiology: uterine artery ligations + selective arterial embolization + hemostasis hysterectomy as a last resort |
| Liver failure and cirrhosis Marker of hepatic synthesis capacity |
Fibrinogen is synthesized exclusively by hepatocytes - it's one of the most sensitive markers of hepatic synthetic capacity, along with albumin, PT (factor V and VII) and cholinesterase; interpretation of fibrinogen in liver disease: healthy liver: fibrinogen 2-4 g/L; mild to moderate acute hepatitis: normal or slightly elevated fibrinogen (acute phase response); fulminant hepatitis or severe acute liver failure: fibrinogen <1.0-1.5 g/L → indicator of extreme severity → criteria for emergency liver transplantation (King's College criteria); compensated cirrhosis: fibrinogen generally maintained until advanced stages (Child-Pugh C); decompensated cirrhosis: fibrinogen <1.5-2.0 g/L → high bleeding risk (esophageal varices + invasive procedures); particularity of cirrhosis - rebalanced coagulation balance: cirrhosis causes both a reduction in pro-coagulant factors (fibrinogen + factors II, V, VII, IX, X) AND anticoagulant factors (protein C + protein S + antithrombin) - prolonged PT and low fibrinogen do not necessarily reflect clinically significant bleeding, as coagulation remains balanced (rebalanced hemostasis concept) - TEG/ROTEM assessment preferable to conventional static workup before any invasive procedure; hepatic acquired dysfibrinogenemia: quantitatively normal but functionally impaired fibrinogen (abnormal sialylation of chains) → Clauss fibrinogen/immunological fibrinogen ratio <0.7 | Management of bleeding risk in cirrhosis: prophylaxis before invasive procedure (ascitic puncture + biopsy + endoscopy + surgery): target fibrinogen >1.5 g/L + platelets >50 G/L (for major surgery or high-risk procedure) → transfusion of fibrinogen concentrate or PFC if necessary; vitamin K 10 mg IV × 3d : useful if prolonged PT due to vitamin K deficiency (cholestasis) - ineffective if true hepatocellular insufficiency (the liver cannot synthesize factors even with available vitamin K); tranexamic acid: controversial use in cirrhosis (may promote mesenteric or portal thrombosis) - avoid except in severe acute hemorrhage under specialized supervision; liver transplantation : only definitive treatment for liver failure - normalization of fibrinogen and coagulation after successful transplantation; biological monitoring of cirrhosis: fibrinogen + PT (INR) + albumin + bilirubin + creatinine = Child-Pugh score + MELD score - fibrinogen monitored every 6 months in compensated cirrhosis + during any acute decompensation |
| High fibrinogen levels - chronic inflammation and cardiovascular risk Acute phase protein - risk marker |
Isolated elevated fibrinogen (without signs of bleeding or thrombosis) most often reflects chronic low-grade systemic inflammation - its interpretation must always be contextualized with the rest of the inflammatory workup (CRP + ESR + CBC + albumin); causes to look for when fibrinogen is chronically elevated (>5 g/L without an acute context): chronic infections (tuberculosis + HIV + viral hepatitis) + chronic inflammatory diseases (RA + IBD + lupus + spondylitis + sarcoidosis) + occult neoplasia (colon cancer + lung cancer + lymphoma - fibrinogen may be elevated before clinical symptoms appear) + active smoking (pro-inflammatory mechanism + direct stimulation of hepatic fibrinogen synthesis) + metabolic syndrome + visceral obesity + type 2 diabetes ; fibrinogen and cardiovascular risk : fibrinogen contributes directly to the pathogenesis of atherosclerosis via several mechanisms - increased blood viscosity + stimulation of smooth muscle cell proliferation + promotion of platelet aggregation + major constituent of unstable atherosclerotic plaques - statins modestly reduce fibrinogen (-0,3-0.5 g/L) via their anti-inflammatory effect (reduction of IL-6) - nicotinic acid (niacin) reduces fibrinogen by 10-15 % but is no longer marketed in Canada; additional work-up for chronic hyperfibrinogenemia: CRP + ESR + CBC + serum protein electrophoresis + TSH + complete metabolic workup + neoplastic screening according to age and risk factors | There is no specific treatment for hyperfibrinogenemia - treatment targets the underlying cause: treatment of chronic inflammatory disease (antirheumatic drugs + biotherapies → normalization of fibrinogen in a few weeks to months); smoking cessation: significant reduction in fibrinogen (-0.3-0.8 g/L) within 6 to 12 months after cessation - one of the most effective measures for reducing elevated fibrinogen from smoking; weight loss (obesity): modest but significant reduction in fibrinogen (-0.1-0.3 g/L per 10 % of weight loss) via reduction in adipokine IL-6; statins: modest reduction in fibrinogen (-5 to -15 %) via anti-inflammatory effect - well-established overall cardiovascular benefit independent of effect on fibrinogen; monitoring: fibrinogen chronically >6 g/L without explanation → thorough work-up in search of occult neoplasia or undiagnosed systemic inflammatory disease; fibrinogen and ischemic stroke: fibrinogen is an independent risk factor for ischemic stroke (increased blood viscosity + thrombosis) - its measurement may be useful in the assessment of cryptogenic stroke in young subjects |
| Fibrinolysis and thrombolytics Post-thrombolysis monitoring - bleeding risk |
Thrombolytic agents (rtPA - alteplase + tenecteplase + streptokinase) massively activate plasminogen to plasmin, which simultaneously degrades thrombus fibrin AND circulating fibrinogen (fibrinogenolysis) - leading to a rapid and profound fall in fibrinogen within hours of administration; indications for thrombolytics requiring fibrinogen monitoring: acute ischemic stroke (IV rtPA within 4.5h) + massive pulmonary embolism + ST-elevation myocardial infarction (thrombolysis if PCI unavailable) + valve prosthesis thrombosis + arterial thrombosis of limbs + central catheter thrombus; post-thrombolysis fibrinogen monitoring: pre-thrombolysis assay (baseline value) + 2h post-perfusion + 6h + 12h + 24h - alarm threshold: fibrinogen <1.0 g/L = major bleeding risk → discontinuation of all anticoagulants + close monitoring + discussion of fibrinogen or cryoprecipitate transfusion if active bleeding; contraindication to thrombolysis if baseline fibrinogen <1.5 g/L (pre-existing coagulopathy); pathological primary fibrinolysis (without DIC): rare - advanced cirrhosis + prostate surgery + liver tumors - direct plasminogen activation without prior coagulation - treatment: tranexamic acid IV 1 g × 3/d - distinction with DIC: ISTH score <5 + moderately elevated (not massive) D-dimer + absence of thrombosis + accelerated euglobulin lysis time (<60 min) | Post-thrombolysis bleeding management: if major bleeding after rtPA (hemorrhagic transformation of stroke + systemic hemorrhage) → immediate discontinuation of rtPA if infusion in progress → fibrinogen concentrate 2-4 g IV (if fibrinogen 2.0 g/L) before resumption; preventive tranexamic acid: prophylaxis in high-risk bleeding surgeries (cardiac + major orthopedic + obstetric) - reduces blood loss by 30-50 % and recourse to transfusions - mechanism: competitive inhibition of plasminogen binding to fibrin → reduction in perioperative physiological fibrinolysis |
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Fibrinogen and pregnancy - a specific interpretation : fibrinogen increases physiologically throughout pregnancy, reaching 4 to 6 g/L in the 3rd trimester - a protective adaptation against the risk of hemorrhage during childbirth. This particularity has two important clinical consequences. On the one hand, a fibrinogen level of 2 g/L in a pregnant woman in the 3rd trimester represents a dramatic drop (-50 to -60 % from expected values) and should trigger an immediate hemorrhagic alert - even though this value would be considered normal in a non-pregnant patient. On the other hand, obstetric DIC (retroplacental hematoma, amniotic embolism, retention of dead fetus) can consume fibrinogen very rapidly from very high levels, making monitoring its kinetics (and not its absolute value) essential in post-partum hemorrhage.
Emergency - Low fibrinogen in a hemorrhagic setting
Dial 911 if : multiple simultaneous bleeds (puncture sites + mucosa + skin) + fibrinogen <1 g/L → open DIC → emergency intensive care.
Postpartum hemorrhage + fibrinogen <2 g/L → emergency transfusion of fibrinogen concentrate - tranexamic acid 1 g IV immediately - call obstetric and haematological team.
Collapsed fibrinogen + jaundice + encephalopathy → fulminant liver failure → urgent transfer to liver transplant center.
Consult at Clinique Omicron
Clinique Omicron doctors prescribe and interpret fibrinogen assays as part of coagulation tests, liver disease monitoring, high-risk pregnancies and inflammatory tests. Abnormal results are referred to the appropriate hematologist, internist or specialist. Consultations are available at several points of service in Quebec and via telemedicine. To book an appointment, visit cliniqueomicron.ca.
The contents of this page are provided for information purposes only and do not replace the advice of a qualified healthcare professional. Interpretation of fibrinogen must always be carried out in the overall clinical context and in correlation with other coagulation parameters.
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